1. Technical Field
The present invention relates generally to semiconductor devices, and more particularly, to a method of forming a silicon-on-insulator (SOI) device having a buried oxide (BOX) layer, and the structure so formed.
2. Related Art
Conventionally silicon-on-insulator (SOI) devices are formed having a buried oxide layer (BOX) under the active regions of a field effect transistor (e.g., a MOSFET device). The BOX layer, which is conventionally made uniformly thin under the active area of the device, produces a faster MOSFET device for several reasons. First, the BOX layer reduces the capacitance between the source/drain regions and the substrate of the device. Second, the channel region, between the source/drain regions, becomes decoupled from the substrate allowing movement, or “floating” of the channel region potential with respect to the substrate. For example, when the channel region potential floats positive, the threshold voltage drops, thereby increasing the drive current.
One of the difficulties typically encountered with this type of device, however, is determining the optimal BOX layer thickness. The capacitance between the source/drain region and the substrate increases as the thickness of the BOX layer is decreased, increasing the circuit loading. The amount of channel region potential “floating” also increases with increasing thickness of the BOX layer due to the reduced capacitance coupling to the substrate. Unfortunately, a floating channel region has the undesirable effect of producing a fluctuating threshold voltage, and therefore, an unpredictable device.
Therefore, there is a need in the industry for a method of forming a semiconductor device that addresses these and other problems.